Saturday, August 25, 2012

U.S. Gulf Coast Vulnerable To Hurricane Isaac

TAMPA, Florida -- Seventy percent of the
Gulf of Mexico shoreline is vulnerable to extreme erosion during even
the weakest hurricanes, according to a report by the U.S. Geological
Survey released just prior to the start of the 2012 hurricane season.

In Florida, the vulnerable coast lines exist from Naples, Florida
northward to Tarpon Springs, Florida on the southwest coast. On the
Florida panhandle, the vulnerability extends from the peninsula of Bald
Point State Park in Franklin County, Florida westward to the Florida
state line near Mobile, Alabama.

All of Alabama's Gulf Coast is vulnerable, and most of the barrier
island and marshes facing the open Gulf south of New Orleans, Louisiana .

Nearly the entire coastline of Texas from Brownsville northward through Galveston, Texas are vulnerable.

USGS scientists used state-of-the-art
modeling to determine the probabilities of erosion, overwash and
inundation during direct hurricane landfall for sandy beaches along the
entire U.S. Gulf Coast shoreline.

The research is expected to help
emergency managers at local, state and federal levels as they prepare
for hurricane events in this and future seasons. Planners will be able
to determine how different categories of hurricanes would impact their
beaches and surrounding communities, helping them better protect lives
and property. The report also includes an interactive map that allows
users to focus on different parts of the Gulf Coast shoreline to view
how the probability of erosion, caused by waves and storm surge, will
vary depending on hurricane intensity.

"The Gulf Coast's beaches provide
abundant recreational opportunities, contribute substantially to the
local economy, and demand the highest real estate values," said USGS
Director Marcia McNutt. "This important research raises awareness on the
specific nature of the vulnerability of these beautiful beaches to
impacts from even Cat-1 hurricanes so that property damage can be
minimized through proper planning."

In a storm, high waves and storm
surge can act together to erode beaches and inundate low-lying lands;
during hurricane landfall, these changes can sometimes be
catastrophic.

"Beaches along the Gulf of Mexico
are extremely vulnerable to erosion during hurricanes, in part, because
of low elevations along the coast," said Hilary Stockdon, a USGS
research oceanographer and lead author of the study. "For example, the
average elevation of sand dunes on the west coast of Florida is eight
feet. On Florida’s Atlantic coast, the average is 15 feet."

During the landfall of a category-1
storm (the expected strength of Hurricane Isaac), where winds are between 75 and 94 miles per hour, overwash is
very likely for 70 percent of Gulf Coast beaches. Overwash occurs when
waves and storm surge overtop dunes and transport sand landward.
Overwash is likely at these locations because of increased water levels
at the shoreline. During category-1 hurricane events on the Gulf Coast,
wave height and storm surge combine to increase water levels at the
shoreline by 14 and a half feet higher than their normal levels.

"People continue to build
communities in coastal areas that shift and move with each passing
storm," said Stockdon. "This model helps us predict the potential impact
of future storms and allows us to identify where the most vulnerable
areas are located along the coast."

Additional findings from the report
show that during a category-1 storm landfall, 27 percent of sandy
beaches along the U.S. Gulf of Mexico are projected to be inundated,
which occurs when increased water levels completely submerge beaches and
dunes. If category-5 storms occur, where winds are 157 miles per hour
or higher, 89 percent of these beaches are likely to be inundated during
a direct landfall.

USGS
scientists used methodology developed from a decade of USGS research on
storm-driven coastal change hazards as the basis for these
calculations. Observational data were combined with sophisticated
hydrodynamic modeling to predict the coastal changes provided in the
report. As new data and storm predictions become available, the report's
analysis will be updated to describe how coastal vulnerability may
change in the future.